refactor: Split all files to enforce 500-line max
Break monolith source files into focused modules:
- stemedb-core/types.rs → types/ directory (assertion, source, gold_standard, etc.)
- stemedb-storage: audit_store, quota_store, trust_rank_store, vector_index, vote_store → module directories
- stemedb-ingest/worker.rs → worker/ with separate test modules
- stemedb-query: engine, materializer, query → module directories
- stemedb-lens: epoch_aware, skeptic → module directories
- stemedb-sim/lib.rs → agent, arenas/, helpers, runner, strategy, types
- stemedb-api/tests: integration_tests → http_basic, http_validation, http_epoch, http_pipeline
- stemedb-api/tests: e2e_flow_test → e2e_full_pipeline, e2e_lens_resolution
- stemedb-query/tests: e2e_pipeline → e2e_pipeline + e2e_decay
Also adds new features: gold standard verification, escalation handlers,
admin endpoints, concept hierarchy spec, arena roadmap, and Go SDK.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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